Water at surfaces and interfaces: From molecules to ice and bulk liquid

The structure and growth of water films on surfaces is reviewed, starting from single molecules to two-dimensional wetting layers, and liquid interfaces. This progression follows the increase in temperature and vapor pressure from a few degrees Kelvin in ultra-high vacuum, where Scanning Tunneling and Atomic Force Microscopies (STM and AFM) provide crystallographic information at the molecular level, to ambient conditions where surface sensitive spectroscopic techniques provide electronic structure information. We show how single molecules bind to metal and non-metal surfaces, their diffusion and aggregation. We examine how water molecules can be manipulated by the STM tip via excitation of vibrational and electronic modes, which trigger molecular diffusion and dissociation. We review also the adsorption and structure of water on non-metal substrates including mica, alkali halides, and others under ambient humid conditions. We finally discuss recent progress in the exploration of the molecular level structure of solid-liquid interfaces, which impact our fundamental understanding of corrosion and electrochemical processes.     

Sharp Error Bounds for Asymptotic Expansions of the Distribution Functions for Scale Mixtures

Let Z be a random variable with the distribution function G(x) and let s be a positive random variable independent of Z. The distribution function F(x) of the scale mixture X = sZ is expanded around G(x) and the difference between F(x) and its expansion is evaluated in terms of a quantity depending only on G and the moments of the powers of the variable of the form s/gr - 1, where (> 0) and (= ±1) are parameters indicating the types of expansion. For = -1, the bound is sharp under some extra conditions. Sharp bounds for errors of the approximations of the scale mixture of the standard normal and some gamma distributions are given either by analysis ( = -1) or by numerical computation ( = 1).     

13C-selective infrared multiple-photon decomposition study of CBrClF2

The infrared multiple-photon single-frequency decomposition (IRMPD) of CBrClF₂ was examined as functions of laser wavenumber, laser fluence, and partial pressure of CBrClF₂. The initial step was the scission of a C-Br bond. In the presence of O₂ the carbon-containing product was CF₂O and its subsequent hydrolysis gave CO₂. The initial dissociation was highly ¹³C selective at wavenumbers below 1014 cm^–1. CBrClF₂ decomposed at relatively low fluences as compared to CHClF₂. However, the decomposition yield rapidly decreased with increasing pressure. In the large-scale irradiation experiment using about 8 J pulse at 1 Hz, we obtained a carbon yield of 0.41 mol per pulse at a ¹³C-atom fraction of 17% for a mixture of 10 Torr CBrClF₂ and 10 Torr O₂, and a carbon yield of 0.17 mol per pulse at a fraction of 29% for a mixture of 20 Torr CBrClF₂ and 20 Torr O₂. The IRMPD of CHClF₂ gave a carbon yield of 0.18 mol per pulse at 48% for 10 Torr neat CHClF₂ and yield of 0.25 mol at 52% for 20 Torr CHClF₂. The large-scale irradiation experiment was also carried out for mixtures of CBr₂F₂ and O₂. CHClF₂ is the most productive of ¹³C.     

Selective synthesis and isolation of all possible conformational isomers of proximally para-disubstituted calix[4]arene

All six possible conformational isomers of the proximally p-dibrominated calix[4]arene tetraalkyl ether, 1a-f*, were selectively synthesized by appropriate control of stereochemistry during di-O-alkylation reactions of 5,11-dibromocalix[4]arene syn-dialkyl ethers, namely, 5,11-dibromo-27,28-dihydroxy-25,26-dipropoxy-, 5,11-dibromo-25,26-dihydroxy-27,28-dipropoxy-, 5,11-dibromo-25,28-dihydroxy-26,27-propoxy-, and 5,11-dibromo-26,28-dihydroxy-25,27-dipropoxycalix[4]arenes. Their conformations were confirmed by (1)H and (13)C NMR spectroscopy and are cone for 1a (u(Br)(Pr), u(Br)(Pr), u(H)(Pr),u(H)(Pr)), partial cone for 1b (u(Br)(Pr), d(Br)(Pr), u(H)(Pr),u(H)(Pr)) and 1d (u(Br)(Pr), u(Br)(Pr), u(H)(Pr),d(H)(Pr)), 1,2-alternate for 1c (u(Br)(Pr), u(Br)(Pr), d(H)(Pr),d(H)(Pr)) and 1e (u(Br)(Pr), d(Br)(Pr), d(H)(Pr),u(H)(Pr)), and 1,3-alternate for 1f (u(Br)(Pr), d(Br)(Pr), u(H)(Pr),d(H)(Pr)). Although both 1c and 1e are in the 1,2-alternate conformation, the conformation of 1e was found to be strongly distorted and distinct from that of 1c.     

The NQR observation of spin-Peierls transition in an antiferromagnetic MX-chain complex [NiBr(chxn)2]Br2

81Br Nuclear quadrupole resonance (NQR) measurement was performed in an S = 1/2 one-dimensional Heisenberg antiferromagnetic metal complex [NiBr(chxn)2]Br2 (chxn: 1R,2R-diaminocyclohexane), having a halogen-bridged MX chain structure -Br-Ni3+-Br-Ni3+-Br-. Two 81Br NQR signals were observed below 40 K, while a single signal was observed above 130 K, showing the presence of two nonequivalent bridging Br sites below 40 K. This NQR result together with previously reported magnetic susceptibility and X-ray results indicate the occurrence of a transition into a spin-Peierls state between 40 and 130 K. This communication reports the first spin-Peierls transition in metal complexes in which pure d electrons contribute to the magnetism. In addition, we demonstrated a new experimental method for studying a spin-Peierls system.     

In vitro replication study of modified bases in ras sequences.

DNA templates containing a modified base (O6-methylguanine, 8-hydroxyguanine, xanthine or hypoxanthine) which was located in nucleotide sequences corresponding to the 12th or 61st codon of a ras gene were synthesized and deoxynucleotide incorporation opposite the lesions was investigated. The templates were replicated by Taq DNA polymerase, recombinant rat DNA polymerase beta and mouse DNA polymerase alpha-primase complex. Sequence analysis of the replicated products indicated selective incorporation of nucleotide(s) opposite a modified base, depending on the kind of base and of DNA polymerase. This system is very useful to obtain results of in vitro replication of modified bases in ras sequences.     

Sulfur-containing polymers. XVIII. Preparation and properties of thiuram polysulfide polymers

Thiuram polysulfide polymers have been prepared from alkali metal bisdithiocarbamates either by oxidation with ammonium persulfate or by polycondensation with sulfur chlorides. In some cases, isothiocyanate formation and/or thiourea formation were noticed. The polymer properties were significantly affected by the diamines used. Polymers derived from p-phenylenediamine decomposed gradually at room temperature with the liberation of elemental sulfur. Polymers based on aliphatic primary diamines were more stable. Piperazine gave the most stable polymer.